The present invention relates to potassium hexatitanate fibers having a tunnel structure and a free potassium content of 5 ppm or less which are useful as a reinforcing material for polyester thermoplastic resins, polyphenylene sulfide resins, liquid crystal polymers, aluminum alloys, magnesium alloys and so forth. The present invention also pertains to a process for producing fibers of this type and to a composite material containing said fibers.
Potassium titanate fibers are whiskers of a substance expressed by the formula K.sub.2 O.nTiO.sub.2 (wherein n=2, 4 or 6). These artificial mineral fibers have applications which have been sought in a wide range of fields such as reinforcing materials, heat-insulating materials, ion exchangers and absorption materials.
Potassium titanate fibers have recently come to be regarded as more and more useful reinforcing materials, particularly for thermoplastic resins, for example, polyamide, polyacetal and ABS resin materials.
However, conventional potassium titanate fibers, which have a relatively high content of potassium that can be liberated from the crystalline structure, have heretofore been unable to exhibit satisfactory reinforcing efficiency when used as reinforcing materials for thermoplastic resins (e.g., polyester resins such as polyethylene terephthalates, polybutylene terephthalates and polycarbonates, polyphenylene sulfide resins, liquid crystal polymers, etc.), aluminum and magnesium alloys and so forth, for the following reasons: (1) free potassium decomposes resin materials of the type described above; and (2) free potassium reacts with aluminum or magnesium alloys.
Thus, the conventional potassium titanate fibers, which have a relatively high free potassium content, are not suitable as reinforcing materials for thermoplastic resins, aluminum and magnesium alloys and so forth, which are easily affected by free potassium.